Defoliation timing and severity in sugar beet

Defoliation produced by different biotic and abiotic factors can reduce sug ar beet (Bera vulgaris L,) sugar content and final yield production. Four t rials were conducted to study the effect on sugar content and yield product ion of systematic defoliations tarried out during the sugar beet growing cy cle, in the Central Ebro Valley in Spain. In two trials, defoliation was ac hieved using shears, a largely untraumatic defoliation method, and in the o ther two by blasting with a pressurized waterjet, producing a traumatic def oliation. Defoliations were performed at seven different growth stages (def ined by heat sums and days from sowing). For each growth stage, four defoli ation levels (control, slight, moderate, and heavy) were imposed. The resul ts revealed a relationship between yield loss, level of defoliation, and gr owth stage when defoliation took place. The most critical growth stage for the effect of defoliation on yield was between 1700 and 1800 degree-days, w hen 100% defoliation produced a 42% yield loss. The higher the Level of def oliation, the higher the yield loss. This study produced a set of regressio n equations that can be used to assess final yield loss caused by defoliati on of sugar beet by such different agents as hail storms, wind, insects, an d other mechanical damage.